Overview

A cholesteatoma, as shown in the images below, consists of an accumulation of desquamated keratin epithelium in the middle ear cleft or any other pneumatized portion of the temporal bone. The envelope of a cholesteatoma is termed a matrix, and desquamated keratin is shed continually by the matrix and forms the central mass of the cholesteatoma, similar to the layers of an onion. The term cholesteatoma is a misnomer, since the entity does not contain cholesterol.

Temporal bone, acquired cholesteatoma. Coronal T1-weighted MRI shows evident integrity of the dura without herniation of brain tissue. Gadolinium enhancement of the mastoid is seen; this corresponds with fibrosis seen at surgery.

In 19 of the patients with AC (63.3%), CT showed a diffuse soft-tissue density isodense with muscle, and in 6 other patients, the mass mimicked inflammation. In the remaining 5 patients with AC, CT revealed a localized soft-tissue mass with partially lobulated contour. Ossicular erosion was detected in 23 AC patients (76.7%), abnormal pneumatization in 19 (63.3%), and erosion-blunting of spur and enlargement of middle ear or mastoid in 8 (26.7%). In the 2 patients with congenital cholesteatomas, CT revealed a soft-tissue mass with polypoid densities, and a semicircular canal fistula was detected in 1 case.
[1]

Diffusion-weighted echo-planar imaging (DW-EPI) has been used to detect residual or recurrent cholesteatoma. Diffusion-weighted imaging (DWI) is a very fast pulse sequence that can usually be performed in less than 1 minute. Cholesteatoma, by virtue of its keratin content, produces high signal intensity compared with brain tissue on DWI obtained with b-values of 800 or 1000 s/ mm2. It has demonstrated a sensitivity of 83% and a specificity of 82% in the diagnosis of residual cholesteatoma, according to a study by Jindal et al. The report involved 50 patients who underwent DW-EPI before surgery. The modality confirmed cholesteatoma in all 15 patients who had a scan before first surgery, and it identified or excluded cholesteatoma correctly in 29 of 35 patients who underwent neuroimaging before second-look surgery.
[2]

Preferred examination

Otoscopic examination is the most important diagnostic technique. In primary acquired cholesteatoma, a retraction pouch is seen in the attic and contains keratin debris. In secondary acquired cholesteatoma, a tympanic membrane perforation is seen in which the epithelium has migrated through the borders and already has reached the middle-ear space. In an infected cholesteatoma, moderate fetid secretions with osteitis and granulation tissue are seen; these can be in the form of inflammatory aural polyps.
[4]

Conventional temporal-bone projections and special imaging procedures, such as high-resolution CT scanning and magnetic resonance imaging (MRI), are employed to complement physical examination and to determine the extent of the disease process, being utilized preoperatively to plan surgical treatment. CT scanning and MRI are useful when revision surgery is performed. High-resolution CT scanning in the axial and coronal planes is the imaging procedure of choice in the diagnosis of temporal-bone cholesteatomas.
[2, 3, 5, 6, 7, 8, 9]

Limitations of techniques

Basically, conventional radiographic studies exhibit great limitations because of the complex anatomy of the temporal bone and the subtle changes induced by small cholesteatomas.

CT scans also have limitations. With CT, it is difficult to differentiate a cholesteatoma from granulation tissue, pus, and fluid, which are present in chronic otitis media without the presence of a cholesteatoma.

The principal limitation of MRI is the lack of bone conspicuity and detail due to the lack of mobile protons in dense cortical bone and signal void experienced when a radiofrequency pulse is applied. Because the major changes induced by a cholesteatoma in the temporal bone are produced within the bony framework, MRI has only a supportive role in the evaluation of subjacent extension of disease outside the confines of the temporal bone, intracranial extension, or rare vascular insult that may occur in large, chronic, or relapsing cases.

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Radiography

Conventional temporal-bone projections remain in use in many parts of the world where CT scanning and MRI are not available. Standard projections for the temporal bone include the Law, Schuller, Mayer, Owen, Chausse III, transorbital, Stenvers, submentovertical, and Towne views. Schuller, Stenvers, Towne, and submentovertical projections are the most useful in the diagnosis of acquired cholesteatoma of the temporal bone.

Schuller view

The Schuller view is a lateral view of the mastoid, obtained with the sagittal plane of the skull parallel to the film and with 30º-cephalocaudal angulation on the radiographic beam. This view shows the degree and extent of mastoid pneumatization, the status of the trabecular pattern, and the position of the lateral sinus.

Stenvers view

The Stenvers view is obtained with the patient facing the film and the head slightly flexed and rotated 45º toward the side opposite the examination. The radiographic beam is angulated 14º caudad. The long axis of the petrous pyramid is parallel to the plane of the film, and the entire pyramid, including its apex, is well visualized. This view shows the entire pyramid, arcuate eminence, internal auditory canal, porus acusticus, horizontal and vertical semicircular canals, vestibule, cochlea, mastoid antrum, and mastoid tip.

Submentovertical view

The submentovertical view (also termed axial or basal) is obtained from under the chin and has the advantage of showing both temporal bones on the same image. In this view, the external auditory canal, eustachian tube, middle ear (including the incus and the head of the malleus), mastoid air cells, styloid process, internal auditory canal, and petrous apex are visualized. This view also demonstrates the foramen ovale, foramen spinosum, and jugular foramen from the base of the skull.

Towne view

The Towne view is an anteroposterior projection with a 30º tilt. As in the submentovertical view, it allows comparison of both petrous pyramids and mastoids in the same image. The petrous apex, internal auditory canals, arcuate eminence, mastoid antrum, and mastoid process can be identified clearly.

High-technology imaging modalities have become the radiologic methods of choice in the study of acquired temporal-bone cholesteatoma.

Degree of confidence

Degree of confidence in radiography is low because of the complex anatomy of the temporal bone and the small radiologic changes induced by pathologic conditions. Interpretation of findings always depends on the experience of the physician.

False positives/negatives

The false-negative rate with plain radiographs is high.

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Computed Tomography

Direct thin-section CT scanning in axial and coronal planes is a must for optimal evaluation of temporal-bone anatomy and pathology. Axial images are obtained parallel to the infraorbitomeatal line to reduce the radiation dose to the lens of the eye.

Direct coronal images can be obtained in supine hanging-head position or prone with the neck extended. Axial images should include the top of the petrous apex to the inferior tip of the mastoid, and coronal images should be obtained from the anterior margin of the petrous apex to the posterior margin of the mastoid.

Contiguous 1- to 1.5-mm–thick sections should be obtained by using conventional sequential acquisition. A spiral technique may be used if a pitch of 1:1 also is used. A small (12-cm) field of view can be applied with scans for each ear, reconstructed separately by using a bone algorithm. Intravenous contrast enhancement is usually not required.

High-resolution CT scanning is ideal for the evaluation of middle-ear pathology. Contrast-enhanced CT scanning also is useful, if an intracranial complication is suspected and/or if a brain hernia (encephalocele) is present in the bed of the revision surgery. (See the image below.)

Advanced technology, such as multidetector-row scanning with submillimeter (0.5-mm) section thickness and high-speed rotation (0.5 second per rotation), has reinforced the benefits of CT scanning in assessing temporal-bone cholesteatomas.

Applications of CT scanning

CT scanning offers high-resolution images with a section thickness of approximately 1 mm, which allows for good visualization of the bony, ossicular, and inner-ear anatomies. On CT scans, good contrast is demonstrated for bone, soft tissue, and air.

CT scanning is the preferred method for evaluating chronic middle-ear disease, including acquired cholesteatoma, because of its ability to demonstrate bony destruction.

CT scanning is used to establish the surgical procedure needed in each patient. CT scanning helps to determine the extent of the cholesteatoma; the location and size of the sac; the status of the ossicular chain; the integrity of the facial canal, tegmen, and sinus plate; and the position of the dura, sigmoid sinus, and jugular bulb. (See the images below.)

Preoperative identification of cholesteatoma is important because it can determine the necessity for surgery and the surgical method. In non–contrast-enhanced temporal bone CT, which is the most commonly used method for preoperative evaluation, soft tissue lesions combined with bony erosion is diagnosed with cholesteatoma.
[10]

CT-scan findings

CT-scan findings in acquired temporal-bone cholesteatoma are characterized by a soft-tissue homogeneous mass with focal bone destruction. Cholesteatoma almost always presents as a complication of chronic otitis media; therefore, the middle-ear space appears cloudy as a result of granulation tissue, pus, and fluid.

Liu and Bergeron have proposed the following CT-scan findings in cholesteatoma
[11] :

Erosion and destruction of the lateral wall of the attic (scutum) (shown in the images below)

Erosion of the roof of the external auditory canal (posterosuperior wall)

The Hounsfield unit (HU) density is a basic characteristic of the CT imaging technique. HU is the linear transition product of the linear attenuation coefficient and is often used for biological tissues. The HU of pure water is 0, that of air is −1000, and that of dense bone is +1000. Every biological tissue has its unique HU, which ranges from −1000 to +1000.
[12]

Min-Hyun Park et al determined the usefulness of CT HU density in the preoperative detection of cholesteatoma in mastoid ad antrum before primary mastoid surgery. The HU was calculated as 42.68 ± 24.42 in the cholesteatoma group and as 86.07 ± 26.50 in the noncholesteatoma group. The differences between the 2 groups were statistically significant (P < .01, Student t test). The sensitivity (51.2-80.5%), specificity (80.5-87.8%), positive predictive value (72.4-86.8%), and negative predictive value (62.3-81.8%) to diagnose cholesteatoma were all shown to improve.
[5]

CT scanning is considerably more sensitive than conventional radiography for detecting cholesteatomas. The overall sensitivity and specificity for detecting residual or recurrent cholesteatoma with CT has been reported to be as low as 42% and 48%, respectively, in one study.
[13]

Granulation tissue and a chronically infected middle-ear mucosa are almost impossible to differentiate from a cholesteatoma.

The cardinal CT sign of cholesteatoma, bony and ossicular erosion, is not applicable in the postoperative ear because of the surgical alteration of the bony and ossicular landmarks. However, CT has a high negative predictive value in a well-aerated middle ear cleft with no evidence of abnormal soft tissue.
[14]

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Magnetic Resonance Imaging

Optimal MRI technique depends on the clinical situation and age of the patient. High–field-strength, contrast-enhanced imaging in the axial and coronal plane has been considered the criterion standard for evaluation of the internal auditory canal (IAC) and inner-ear structures.
[7]

Nonenhanced and gadolinium-contrast–enhanced T1-weighted images are compared in order to differentiate bright lesions (fat and blood products) from enhancing lesions visualized after contrast infusion. Three-dimensional (3D) fast spin-echo T2-weighted images allow high-resolution imaging of the IAC and labyrinth. A variety of 3D gradient-echo techniques with thin sections also are available.

The MRI characteristics of acquired temporal-bone cholesteatoma are demonstrated in the images below.

Temporal bone, acquired cholesteatoma. T1-weighted axial MRI shows a soft-tissue mass in the region of the right tegmen tympani.

Gadolinium-based contrast agents have been linked to the development of nephrogenic systemic fibrosis (NSF), also known as nephrogenicfibrosingdermopathy (NFD). The disease has occurred in patients with moderate to end-stage renal disease after they were given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography scans. NSF/NFD is a debilitating and sometimes fatal disease.

Characteristics of NSF/NFD include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness.

Applications of MRI

The role of MRI in the evaluation of middle-ear pathology is limited. The most important contributions of MRI to the study of acquired temporal-bone cholesteatoma are the following:

Precise definition of the borders of large lesions

Depiction of the relationship of the lesion to intracranial structures

Help in evaluating intratemporal and extratemporal complications

Follow-up in patients who have undergone middle-ear surgery for a cholesteatoma

MRI defines the integrity of the dura, which is best appreciated with T2-weighted sequences, without the need for contrast material. However, in cases of dural infection, subtle contrast enhancement may be the only clue that dural involvement is present.

MRI delineates intracranial extension of the cholesteatoma or protrusion of the intracranial contents into the middle ear, when defects of the tegmen tympani or sinus plate are visualized on the CT scan. MRI is also indicated when the facial nerve is involved.

MRI findings

MRI is also used to differentiate cholesteatomas from other temporal-bone lesions, such as cholesterol granulomas, granulation tissue, inflammatory mucosa, and scar tissue.

Cholesterol granulomas produce high signal intensity on both sequences, with no contrast enhancement. Granulation tissue and inflammatory mucosa generally produce a hypointense or intermediate signal on T1-weighted images and a hyperintense signal on T2-weighted images with contrast enhancement. Because of its fibrous nature and, possibly, the microvascular thrombosis phenomenon, it is necessary to obtain delayed contrast-enhanced images with a delay of 30–45 minutes after contrast-material administration.
[16]

A study by Dubrulle et al showed the reliability of diffusion-weighted, fast spin-echo MRI in the detection of recurrent cholesteatoma in patients who have undergone middle-ear surgery.
[17] Recurrent cholesteatoma was diagnosed if the lesion had low signal intensity on unenhanced T1-weighted images, showed no change in signal intensity on delayed contrast-enhanced T1-weighted images, and had high signal intensity on diffusion-weighted images obtained with a b factor of 800 sec/mm2.

The negative predictive value was 100%, which means that patients who show no signs of recurrent cholesteatoma on diffusion-weighted fast spin-echo images may not need second-look surgery.

Imaging of postoperative middle ear cholesteatoma

Cholesteatoma is often treated surgically using canal wall-preserving techniques. Clinical and otoscopic diagnosis of residual or recurrent disease after this form of surgery is unreliable and thus radiological imaging is often used prior to mandatory “second-look” surgery.

Imaging needs to be able to differentiate residual or recurrent disease from granulation tissue, inflammatory tissue, or fluid within the middle ear cavity and mastoid cavity. High-resolution CT (HRCT), conventional MRI, and delayed-contrast MRI have all been used in detecting postoperative cholesteatoma.

Although delayed-contrast MRI performs better than HRCT and conventional MRI, the sensitivities and specificities of these different imaging methods are relatively poor. DWI, in particular, nonecho planar DWI, has been shown to have high sensitivity and specificity for detecting recurrent cholesteatoma.
[18]

Delayed-contrast MRI

Several authors have investigated the use of delayed contrast-enhanced MRI scans for the detection of residual or recurrent cholesteatoma following surgery.

Obtaining images after a delay of 30-45 minutes results in enhancement of granulation tissue or scar tissue within the operated middle ear cleft. Cholesteatoma, on the other hand, is nonenhancing and can therefore be differentiated from granulation or scar tissue. Delayed-contrast MRI has been reported to detect cholesteatoma greater than 3 mm. However, the diagnostic performance with this technique in detecting cholesteatoma is extremely variable, with an overall sensitivity and specificity of 14-90% and 55-100%, respectively.
[19]

Degree of confidence

MRI is considerably more sensitive than conventional radiography, but it is less sensitive than high-resolution CT scanning, because of the lack of bone delineation on MRI.

Temporal bone, acquired cholesteatoma. Coronal CT of right cholesteatoma. A large soft-tissue mass in the right middle ear extending medial to the ossicles. The scutum is eroded and tympanic membrane is retracted. Note associated erosion of tegmen tympani. The normal left ear is shown for comparison.

Temporal bone, acquired cholesteatoma. Axial CT scan of left cholesteatoma. A soft-tissue mass in the middle ear with destruction of ossicles and erosion of the walls of middle ear cavity.

Temporal bone, acquired cholesteatoma. Axial CT scan of right cholesteatoma shows a large cavity in the right mastoid air cells; this is consistent with an automastoidectomy.

Temporal bone, acquired cholesteatoma. This image shows the integrity of the mastoid tegmen.

Temporal bone, acquired cholesteatoma. Axial MRI was used to identify the integrity of the brain tissue and a small right temporal-bone cholesteatoma. This produces a low signal intensity on T1-weighted images and high signal intensity on T2-weighted images and, sometimes, peripheral contrast enhancement.

Temporal bone, acquired cholesteatoma. Coronal T1-weighted MRI shows evident integrity of the dura without herniation of brain tissue. Gadolinium enhancement of the mastoid is seen; this corresponds with fibrosis seen at surgery.